1. Field of the Invention
The present invention relates to a fuel cell, a fuel supply apparatus therefor, and a fuel supply system therefor.
2. Description of the Related Art
Recently, various portable devices use fuel cells as the power source. Among many proposals for fuel cells, direct methanol fuel cells (DMFCs), in which an organic fuel, such as methanol, is directly supplied to the anode to generate power, are primary candidates for the power sources of portable devices. This is due to the fact that DMFCs do not require a reformer for reforming the organic fuel, such as methanol, to a hydrogen-rich reformed gas, and thus have a simple structure. Several proposals have been made as to the details of DMFCs (e.g., Japanese Patent Laid-Open No. 2002-056857). The operation of DMFCs can be briefly described as follows. In a typical operation, air is supplied to the cathode while supplying the organic fuel to the anode, during which the reaction described below occurs:CH3OH+H2O→CO2+6H++6e+  (1)
Protons (H+) generated at the anode travel to the cathode via a solid polymer membrane, i.e., an electrolyte, to react with oxygen in air as below:O2+4H++4e+→2H2O  (2)Water and carbon dioxide are generated as a result of power generation.
Other than DMFCs, fuel cells that generate power by directly supplying hydrogen stored in a hydrogen-absorbing alloy or a carbon nanotube have been proposed.
Fuel cells can generate power by simply supplying a fuel and an oxidant and can continuously generate power by replacing the fuel. Whereas secondary batteries require several hours of recharging, fuel cells can be restored instantly. Thus, the system employed in fuel cells is particularly advantageous for application to portable devices having low energy consumption.
An example that uses a fuel cell unit as the power source of a portable computer is disclosed in Japanese Patent Laid-Open No. 9-213359. In the disclosure, a system in which generated water is stored and vaporized is described in addition to basic structures such as air inlet and outlet, a fuel bottle, terminals, power generation section, and the like.
Moreover, use of fuel cells as the power source of portable computers is also known. For example, Japanese Patent Laid-Open No. 2002-49440 teaches fuel cells, whose fuel is supplied in the form of a cartridge.
However, the above-described conventional examples have the following problems. Since fuel cells inevitably produce water, the water must be discharged, removed by vaporization, or the like. Water may reach the inside of the portable device, such as a portable camera, and may thereby damage the device.
The invention set forth in Japanese Patent Laid-Open No. 9-213359 described above prevents water from affecting the portable computer. According to the disclosed structure, an internal water-retaining unit is installed inside the fuel cell unit. A water-retaining tank is also provided in case the water-retaining unit is not large enough. The water-retaining tank is detachable and the water-retaining unit is replaceable. However, according to this structure, when the fuel is replaced with new fuel, the fuel cell must be disassembled, the water-retaining tank must be separated to discharge water, and water in the water-retaining unit must be removed by drying before reassembling the fuel cell. This process is cumbersome and complicates the system. Moreover, leakage of water may result from neglect to discharge water, misassembly, or the like.
The invention set forth in Japanese Patent Laid-Open No. 2002-49440 above provides a method for discharging the produced water from a personal computer equipped with fuel cells without damaging the personal computer. However, the method uses an exhaust hose and thus cannot be applied to cameras, cellular phones, etc.